Question

How do you factor 9x^3 + 64
(Please show steps)

Answer 1

First, let's review the formula for the "sum of two cubes:"

a^3 + b^3 = (a + b)(a^2 - ab + b^2).

Unfortunately, 9 is not a perfect cube. The cube root of 9 is 9^(1/3), and the square of the cube root of 9 is therefore 9^(2/3).

Thus,

9x^3 + 64 = (9^(1/3)*x + 4) * (9^(2/3)x^2 - 4*9^(1/3) + 16)